bird thruline watt meter bird thruline bird thruline model 43 wattmeter bird 43 thruline bird 43 thruline wattmeter bird 43 thruline wattmeter element bird 43 thruline wattmeter line section bird 43 thruline wattmeter element 5w 5a 25-60mhz bird 43 thruline wattmeter element 25-60mhz bird 43 thruline wattmeter dual line section